To be honest, the best thing to do if you are encountering this problem regularly is just to force close the app after you exit it. This is as easy as pressing the recent apps button and swiping it off the list. You may want to wait a few seconds to give the app time to gracefully close though. That should hopefully allow you to open it again immediately if needed. Otherwise you might want to wait 10-15 seconds to see if that helps if you'd rather not force kill it. It's weird that you are encountering this issue at all though... Another user just reported it happening on a chromebook, so I'm beginning to wonder if this problem is only exhibited on certain devices, or if there something I might need to change.
Mike
Mike